1. Field of the Invention
The present invention relates to an arrangement for insuring uninterrupted current supply to at least one electrical consumer, whose energy is taken from an a.c. power supply network and which is supplied with energy from a fuel cell in case of a network outage.
2. Prior Art
An arrangement of this type is known from the NTT Review, vol. 6, no. 2, Mar. 1, 1994, pages 47 to 53, XP000446893, Asano N. et al.: "The future of our fuel cell total energy system". During continuous operation, a PAFC (phosphoric acid fuel cell) is connected there parallel with an a.c. voltage network. If the a.c. voltage network fails, the fuel cell takes on the supply of energy.
A further arrangement is known from DE-PS 16 00 027. In connection with this arrangement a first rectifier is connected to an a.c. voltage network. A capacitor and a consumer are connected in parallel with the output of a comparator. The consumer is furthermore connected via a switch to a fuel cell. The output of a second rectifier, which is also supplied by the a.c. voltage network, is furthermore connected in parallel with the fuel cell. The second rectifier generates a countervoltage corresponding to the output voltage of the fuel cell in order to keep the gas consumption of the fuel cell as low as possible when the network voltage is intact.
It is known from the book "Brennstoffelemente" [Fuel Elements], Verlag Chemie GmbH, Weinheim, Bergstra.beta.e, 1965, p. 368, to employ fuel cells as emergency power installations.
Interruption-free current supply arrangements are used to supply consumers, whose outage because of the loss of supply voltage leads to an impermissible and undesirable disruption of an operation. Some operations are already endangered by a voltage collapse of short duration. Voltage collapses in a supply network can be caused by ground faults or short circuits, line interruptions or switching processes. Interruption-free current supply arrangements are used in hospitals, for example, where an outage of the public network can endanger the life and health of people. Interruption-free current supply arrangements are also practical for preventing property damage in case of network outage. Interruption-free current supply arrangements should be differentiated from network replacement arrangements, which assure the power supply during extended network outages. Interruption-free current supply arrangements already take over the power supply in case of network outages of a few milliseconds for a tiding-over period of a few minutes up to 15 minutes or more.
Rechargeable batteries are used as energy reservoirs for interruption-free current supply installations. With some installations, these batteries are the main energy reservoirs, and with others they are short-term reservoirs in connection with Diesel units. Generally, closed lead batteries with a liquid electrolyte, closed lead batteries with a fixed electrolyte or NiCd batteries are used. Control and monitoring devices must be provided in an interruption-free current supply arrangement, by means of which interruptions which cause the outage of the battery are detected and prevent the deep charging along with overcharging of the battery.
The outage of the battery must be detected and reported in good time. The charging unit must recharge the battery within a defined period of time, because of which the interruption-free current supply arrangement cannot remove energy from the battery for this period of time.